Related fields include diffusion barrier layers in semiconductor devices, particularly those for blocking the diffusion of copper and oxygen.
As the feature sizes of microelectronic assemblies (e.g., integrated circuits) continue to decrease, manufacturing challenges emerge. For example, diffusion barrier layers are often used between conductive interconnects or vias, often made of copper, and the surrounding interlayer dielectric (ILD) materials, such as silicon dioxide or other insulating materials. Without the diffusion barrier, the copper may diffuse into the ILD, compromising its insulating properties; likewise, materials from the ILD, such as oxygen, may diffuse into the copper and compromise its conductive properties. Therefore, diffusion barrier layers may need to have low diffusion coefficients (<10−8 cm2/s).
As the interconnects and vias decrease in size and increase in density, the diffusion barrier layers, quite thin to begin with, must scale proportionally with the vias, trenches, and interconnects; i.e., they must become even thinner to fit in the available space. Moreover, because the smaller features are often more sensitive to contamination, such new thinner diffusion barrier layers must perform at least as well as, and preferably better than, their thicker predecessors.
Besides blocking diffusion into and out of the interconnects, these diffusion barriers preferably have low resistivity to assist the interconnect in carrying current, and good adhesion to copper so that thin copper layers do not agglomerate (become non-contiguous) when the substrate is heat-treated during processing.
A bi-layer diffusion barrier of tantalum nitride (TaN) and metallic tantalum (Ta) is presently used in many integrated circuit devices. The TaN blocks diffusion and the Ta provides an interface for copper adhesion. Copper layers thinner than about 20 nm tend to agglomerate during annealing if they are deposited directly on TaN, and Ta by itself does not sufficiently block diffusion. Both the TaN and the Ta performance degrade as the layers become thinner.
Often a thin “seed layer” will be deposited on the diffusion barrier layer before forming the interconnect. Many current devices use a copper seed layer. If the seed layer could contribute to diffusion blocking and adhesion promotion, it could relax some of the demands on the diffusion barrier layer.
Therefore, a need exists for materials that block diffusion and provide adhesion for copper at smaller thicknesses. If a single layer of material could provide both diffusion blocking and adhesion, it would simplify manufacturing and reduce cost. If a seed layer could perform an extra function of diffusion blocking or adhesion promotion, it would allow diffusion barrier layers to be even thinner, and/or to be eliminated completely.